THE REGION OF THE ORBIT. 41 



men and anterior lacerated fissure. Each surface splits 

 into two layers one continuous with the pericranium at 

 the upper margin of the circumference, or with the peri- 

 osteum of the face, and the other which forms the pal- 

 pebral ligament of the lids. The muscles which act upon 

 the globe are six in number namely, the four recti and 

 two obliqui, and one muscle acting upon the upper lid, 

 the levator palpebraB. These muscles are inclosed in 

 fibrous sheaths derived from the orbital aponeurosis. At 

 their insertion their tendons become expanded upon and 

 continuous with the sclerotic. The complete division of 

 the aponeurotic sheaths as well as of the tendons is nec- 

 essary in the operation for strabismus, as these invest- 

 ments if left undivided still exert considerable power 

 over the globe, owing to their completely inclosing both 

 muscle and tendon. The recti tendons are inserted into 

 the sclerotic about a quarter of an inch behind the cor- 

 nea. The upper and lower eyelids are united to the 

 sheaths of the superior and inferior recti muscles by an 

 oifset of the palpebral aponeurosis, forming the posterior 

 boundaries of the superior and inferior oculo-palpebral 

 cul-de-sacs. A knowledge of the arrangement of these 

 aponeurotic expansions and of their situations is of some 

 considerable importance in the diagnosis of intra-orbital 

 injury or disease, as by their attachment and situation 

 they facilitate or impede the course taken by blood or 

 pus. Ecchymosis beneath the conjunctiva is almost in- 

 variably a symptom of fracture of the roof of the orbit 

 after injury of the head. 



The eyeball and its vessels and nerves lie in a mass of 

 fat and cellular tissue, which serves as a cushion for the 

 optic nerve and for the globe in its various movements, 

 and as a support for its accessory structures. This eel- 



